In electronic devices, very fine soiling can cause operating faults or a deterioration in performance, and therefore it is desirable that microscopic soiling on substrates for electronic devices such as semiconductor substrates, hard disk substrates and display substrates used for liquid crystal panels and the like is effectively completely removed. Accordingly, in precision cleaning processes used within the industrial field, any soiling adhered to substrates for electronic devices must be removed with a very high degree of cleanliness.
Examples of the soiling include organic soiling derived from substrate fixing agents such as waxes and the like, particulate soiling derived from polishing agents such as colloidal silica, metal soiling derived from metals such as Fe, Na or Cu, or metal ions thereof, and mixtures of these different soiling types.
A multitude of precision cleaning techniques have been proposed for achieving the required degree of cleanliness, depending on the type of electronic device substrate that is to be cleaned and the nature of the soiling adhered to the electronic device substrate.
For example, in the case of precision cleaning of semiconductor substrates, a method that involves performing cleaning treatments with hydrogen peroxide and a strong acid (such as sulfuric acid or hydrochloric acid), hydrogen peroxide and an alkali (such as ammonia), and hydrofluoric acid, the so-called “RCA cleaning” method, is widely used (for example, see Non-Patent Document 1).
Further, an example of another cleaning method besides the RCA cleaning method described above is a cleaning method in which the oxidizing power of ozone is used to remove organic soiling (for example, see Patent Document 1).    [Non-Patent Document 1]    RCA Review, p. 187, June 1970    [Patent Document 1]    Japanese Laid-Open Patent Application No. 2002-231677